That can come in handy, too. But you want to restrict this to pinned topics, a certain category and / or topics with a tag from a visible-to-everyone-but-can-only-be-used-by-xyz group. Otherwise people could easily miss that a discussion was closed because it got out of hand.
Yes, like this:
While you cannot post a reply in this closed topic, feel free to start a new topic or include any quotes in another open one.
But my primary request has been that mods can change a topic so that replying to it defaults to start a new topic. To avoid confusion the preview window could display a message like:
To keep this central topic clean and clear, please start a new topic on the aspect you wish to discuss. Use a meaningful title and include quotes as appropriate. Create multiple topics, if you wish to discuss unrelated items.
At the end of the day, I do not mind if such a Hub Topic is open or closed. But curator(s) need to be able to reply in the topic when they lack moderator-privileges, whereas everybody else is encouraged to start a new topic (if it does not already exist).